Method of forming an interconnection structure in a organosilicate glass having a porous layer with higher carbon content located between two lower carbon content non-porous layers

ABSTRACT

Interconnect structures possessing a non-porous (dense) low-k organosilicate glass (OSG) film utilizing a porous low-k OSG film as an etch stop layer or a porous low-k OSG film using a non-porous OSG film as a hardmask for use in semiconductor devices are provided herein. The novel interconnect structures are capable of delivering improved device performance, functionality and reliability owing to the reduced effective dielectric constant of the stack compared with that of those conventionally employed and also because of the relatively uniform line heights made feasible by these unique and seemingly counterintuitive features. The present invention also provides a fluorocarbon-based dual damascene etch process that achieves selective etching of a dense low-k OSG films relative to that of a porous low-k OSG film owing to the tunability of the gas-phase fluorine:carbon ratio (gas dissociation) and ion current below a critical threshold and given the larger carbon content of the porous film relative to that of the dense film.

RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.10/845,718, filed May 14, 2004.

FIELD OF THE INVENTION

The present invention generally relates to semiconductor integratedcircuits (ICs), and more particularly to semiconductor interconnectstructures, including multilevel interconnect structures, in whichadvanced dual damascene processing enables using a porous low-kdielectric material as an etch stop layer (ESL) for a non-porous (dense)low-k dielectric film, or using a non-porous (dense) low-k dielectricfilm as a hardmask for a porous low-k dielectric material. The term“low-k” is used throughout the present application to denote aninsulator having a dielectric constant of less than silicon dioxide,i.e., less than about 4.0. All dielectric constant values are measuredin a vacuum unless otherwise specified herein.

BACKGROUND OF THE INVENTION

Currently, semiconductor devices include a plurality of circuits, whichform an integrated circuit (IC) including chips (e.g., chip back end ofline, or “BEOL”), thin film packages and printed circuit boards.Integrated circuits can be useful for computers and electronic equipmentand can contain millions of transistors and other circuit elements thatare fabricated on a single silicon crystal substrate. For the device tobe functional, a complex network of signal paths will normally be routedto connect the circuit elements distributed on the surface of thedevice. Efficient routing of these signals across the device can becomemore difficult as the complexity Efficient routing of these signalsacross the device can become more difficult as the complexity and numberof integrated circuits are increased. Thus, the formation of multilevelor multilayered interconnection schemes such as, for example, dualdamascene wiring structures, have become more desirable due to theirefficacy in providing high speed signal routing patterns between largenumbers of transistors on a complex semiconductor chip. Within theinterconnection structure, metal vias run perpendicular to the siliconsubstrate and metal lines run parallel to the silicon substrate.

Presently, interconnect structures formed on an integrated circuit chipconsists of at least about 2 to 8 wiring levels (See, for example,FIG. 1) fabricated at a minimum lithographic feature size designatedabout 1× (referred to as “thinwires”) and above these levels are about 2to 4 wiring levels fabricated at a width equal to about 2× and/or about4× the minimum width of the thinwires (referred to as “fatwires”). Inone class of structures, the thinwires are formed in a low dielectricconstant (k) organosilicate glass (OSG) dielectric layer, and thefatwires are made in a silicon dioxide dielectric layer having adielectric constant of about 4. The OSG typically contains elements ofSi, C, O and H, and is sometimes referred to as SiCOH dielectrics. Thesedielectrics have a dielectric constant that is below 4.0, typically thedielectric constant of OSG dielectrics is between 2.8-3.1.

In typical trench or via-first integration strategies, one of thechallenges during the creation of the line level structure in dualdamascene processing is to minimize line height variations (and henceline resistance variance) within a wafer and within a lot. These lineheight variations can arise owing to occasional etch ratenon-uniformities within the employed plasma process dependent on patterndensity and/or feature aspect ratio variations or due to variations inthe interlevel dielectric (ILD) film thickness. To compensate for sucheffects, an etch stop layer (ESL) for line levels (M_(x+1) levels, wherex is a positive integer) can be desirable for maintaining within waferand within lot uniformity such that line resistance values are withindesign manual specifications with minimal variability; thus enabling amore manufacturable process.

Typical ESLs employed for alleviating such effects include variouspermutations of SiC (SiCN_(x)H_(y)) or Si₃N₄ (SiON) are of higherdielectric constant (k≧5.0) than that of the ILD materials employed for90 nm back-end-of-the-line (BEOL) technologies (k of approximately 2.8to 3.1); thus, though addressing the issue of line height uniformity andline level resistance variance, prior art ESLs decrease overall deviceperformance by increasing the effective dielectric constant, k_(eff), ofthe structure.

In addition to the above problem concerning prior art ESLs, there is anongoing trend of replacing traditional ILDs with low-k dielectrics thatare porous. The use of porous ILD materials for 65 nm and subsequentBEOL technologies also introduces the concept of line height control andconsequent variance in metal line resistances. Since typically BEOLprocessing conditions would etch a low-k dielectric hardmask faster thanthe underlying porous low-k material, the issue in line height controland resistance variation is perhaps made even more severe for thesetechnologies.

In view of the above drawbacks with prior art interconnect structures,there is a need for providing new and improved interconnect structuresin which the line height variation and hence the line resistancevariance is minimized.

SUMMARY OF THE INVENTION

The present invention provides a BEOL interconnect structure, e.g., adual damascene interconnect structure, in which a porous organosilicateglass (OSG) comprising elements of Si, C, H and O is employed as an etchstop layer for non-porous (dense) OSG interlevel dielectrics. The OSGmaterial is a hydrogenated oxidized silicon carbon material alsoreferred to in the art as a carbon doped oxide. The present inventionalso provides a BEOL structure in which a non-porous (dense) OSGdielectric is employed as a hardmask for a porous OSG interleveldielectric. The porous and non-porous OSG dielectrics employed in thepresent invention are both low-k dielectrics.

In accordance with the present invention, the BEOL interconnectstructures of the present invention have minimized line height variationand minimal line resistance variation. More particularly, the inventiveBEOL interconnect structures have improved device functionality andperformance due to the reduced effective dielectric constant, k_(eff),of the overall BEOL stack compared with conventionally employed BEOLstacks.

In one aspect of the present invention, the interconnect structurecomprises a porous organosilicate glass etch stop layer located betweenfirst and second non-porous organosilicate glass interlevel dielectrics,said porous organosilicate glass having a carbon content that is greaterthan the carbon content present in said first and said second non-porousorganosilicate glass interlevel dielectrics.

In another aspect of the present invention, the BEOL interconnectstructure comprises at least one porous organosilicate glass interleveldielectric and a non-porous organosilicate glass hardmask located on asurface thereof, said at least one porous organosilicate glassinterlevel dielectric having a carbon content that is greater than thecarbon content in said non-porous organosilicate glass hardmask.

In addition to the above mentioned BEOL interconnect structures, thepresent invention also provides methods to fabricate such structures. Inbroad terms, one method of the present invention comprises the steps of:

providing a structure comprising a porous organosilicate glass etch stoplayer located between a first non-porous organosilicate glass interleveldielectric and a second non-porous organosilicate glass interleveldielectric, said porous organosilicate glass having a carbon contentthat is greater than the carbon content in the first and secondnon-porous organosilicate glass interlevel dielectrics; andpatterning said structure to provide an opening that extends through thestructure, said patterning comprising lithography and etching, whereinsaid etching is performed in a fluorocarbon-based plasma having afluorine to carbon ratio and at an ion current that selectively etchesthe non-porous organosilicate glass interlevel dielectrics relative tothe porous organosilicate glass.

Following patterning, a conductive metal or metal alloy can be formedwithin the opening providing a conductively filled region within thepatterned structure.

Another method of the present invention comprises the steps of:

providing a structure comprising a non-porous organosilicate hardmasklocated on a porous organosilicate glass interlevel dielectric, saidporous organosilicate glass having a carbon content that is greater thanthe carbon content in the non-porous organosilicate glass; andpatterning said structure to provide an opening in the structure, saidpatterning comprising lithography and etching, wherein said etching isperformed in a fluorocarbon-based plasma having a fluorine to carbonratio and at an ion current that selectively etches the non-porousorganosilicate glass hardmask relative to the porous organosilicateglass interlevel dielectric.

Following patterning, a conductive metal or metal alloy can be formedwithin the opening providing a conductively filled region within thepatterned structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pictorial representation (through a cross sectional view)showing a prior art 5 level metal interconnect structure.

FIG. 2 is a pictorial representation (through a cross sectional view)showing a pre-metalized dual damascene interconnect structure built in anon-porous (dense) organosilicate glass material with a trench-level(M_(x+1)) porous etch stop layer.

FIGS. 3A-3B are pictorial representations (through cross sectionalviews) of a dual damascene structure built in a porous low-korganosilicate glass dielectric material employing a trilayer resistscheme in which FIG. 3A is post lithography structure and FIG. 3B is apost partial etch structure.

FIGS. 4A-4B are cross sectional scanning electron micrographs (SEMs) ofvarious dual damascene interconnect structures built in a porous OSGdielectric with TEOS and SiCOH hardmask showing a 28 nm line heightsubsequent to 45 seconds of the inventive trench etch and a 41 nm lineheight subsequent to 60 seconds of the inventive trench etch,respectively.

DETAILED DESCRIPTION OF THE INVENTION

The present invention, which provides interconnect structures possessinga non-porous (dense) low-k organosilicate glass (OSG) film utilizing aporous low-k OSG film as an etch stop layer or a porous low-k OSG filmusing a non-porous OSG film as a hardmask, as well as methods forfabricating such structures, will now be described in greater detail byreferring to FIGS. 2-4 that accompany the present application. It shouldbe noted that the dual-damascene structures shown in FIGS. 2 and 3A-3Bare not drawn to scale. Moreover, these structures are provided forillustrative purposes only. Hence, the present invention is not limitedto the interconnect structure specifically shown. Instead, the presentinvention can be used in forming any interconnect structure that isknown in the art.

Reference is first made to FIG. 2 which shows a pre-metallization dualdamascene interconnect structure 10 that includes substrate 12 having aconductive metal region 14 formed therein, and a dielectric cap 16located on top of substrate 12 and conductive region 14. Theinterconnect structure 10 also includes a first non-porous OSGinterlevel dielectric 18 located atop the dielectric cap 16, a porousOSG etch stop layer 20 located atop the first non-porous OSG interleveldielectric 18, a second non-porous OSG interlevel dielectric 22 locatedatop the porous OSG etch stop layer 20 and at least one opening 24. Asshown, opening 24 extends through the second porous OSG interleveldielectric 22, the porous OSG etch stop layer 20, the first non-porousOSG interlevel dielectric 18, and dielectric cap 16, stopping on anupper surface of conductive region 14.

In accordance with both embodiments of the present invention, the porousOSG material has a carbon content that is greater than the non-porousOSG material. Typically, the porous OSG material has a carbon contentfrom about 8 to about 18 atomic %, whereas the non-porous OSG has acarbon content from about 8 to about 13 atomic percent. More typically,the porous OSG has a carbon content from about 12 to about 15 atomic %,whereas the non-porous OSG has a carbon content from about 9 to about 11atomic percent.

The substrate 12 of interconnect structure 10 may include anyconventional material in which a conductive region can be formed. Thus,for example, substrate 12 may be a dielectric material such as aninorganic or organic, porous or non-porous, dielectric, or asemiconductor substrate such as Si, SiGe, GaAs, InAs, SiC, SiGeC, InPand other III/V or II/VI compound semiconductors. Substrate 12 can alsobe a silicon-on-insulator (SOI), a silicon germanium-on-insulator (SGOI)or any other layered semiconductor material. When a semiconductorsubstrate is employed as substrate 12, the substrate 12 may includevarious circuits and/or devices. For clarity, the circuits and/ordevices are not shown in FIG. 2.

The conductive region 14 comprises at least one conductive metal. Theterm “conductive metal” includes, but is not limited to: metals such asaluminum (Al), copper (Cu), tungsten (W), silver (Ag) and other likemetals that are electrically conductive and are used in interconnectstructures. Alloys of these conductive metals such as Al—Cu are alsocontemplated herein. A preferred metal for conductive region 14 is Cu.

The conductive region 14 is formed utilizing conventional processingthat is well known in the art, including, for example, lithography,etching and trench fill. The trench fill step includes a depositionprocess such as, for example, chemical vapor deposition (CVD),plasma-assisted CVD, plating, sputtering, chemical solution depositionand other like deposition processes. A planarization process such aschemical-mechanical polishing (CMP) or grinding typically follows thetrench fill process.

An optional liner material, not shown, can be formed within the etchedtrench prior to trench fill. The optional liner material preventsdiffusion of the conductive metal into the dielectric layers. Someexamples of such liners include, but are not limited to: TiN, TaN, Ti,Ta, W, WN, Cr, Nb and other like metal diffusion barrier liners andcombinations thereof. The optional liner can be formed in the trenchusing well known deposition processes including, for example, CVD,plasma-assisted CVD, sputtering, plating and chemical solutiondeposition.

After providing the substrate 12 including conductive region 14, adielectric cap 16 is formed atop the structure. Specifically, thedielectric cap 16 is formed atop exposed surfaces of both substrate 12and conductive region 14. The dielectric cap 16, which serves as adiffusion barrier in the inventive interconnect structure, is formed inthe present invention utilizing a conventional deposition processincluding, for example, CVD, plasma-assisted CVD, evaporation, spin-ondeposition, chemical solution deposition and the like. The dielectriccap 16 may comprise an inorganic dielectric such as an oxide, nitride,oxynitride or carbide, or dielectric cap 16 may comprise an organicdielectric having a dielectric constant below 4.0. Examples of organicmaterials that can be employed as dielectric cap 16 include, but are notlimited to: polyarylenes. In some embodiments of the present invention,dielectric cap 16 is omitted. In embodiments in which dielectric cap 16is present, the dielectric cap 16 typically has a deposited thicknessfrom about 25 to about 50 nm.

Next, first non-porous OSG 18, porous OSG layer 20 and second non-porousOSG layer 22 are formed. The porous OSG layer 20, which in accordancewith the present invention has a higher carbon content than thenon-porous OSG layers 18 and 22, serves as an etch stop layer in thestructure shown in FIG. 2. The pore size present in the porous OSG 20may vary and is not critical to the present invention. Typically, andfor illustrative purposes, the porous OSG etch stop layer 20 has a poresize ranging from 0.5 to about 8 nm at a volume percent from about 10 toabout 50%.

The various OSG material layers are formed by any deposition techniquesuch as CVD or plasma-enhanced CVD, in which at least a first precursor(gas, liquid or vapor) containing atoms of Si, C, O and H is employed.An optional second precursor (gas, liquid or vapor) comprising mainlyatoms of Si, and C and optionally F, N and O can be employed. The firstprecursor utilized may be selected from one or more molecules containingat least atoms of Si, C, O and H. Oxidizing molecules such as O₂ or N₂Ocan be added to the first precursor. Preferably the first precursor is asiloxane containing Si, C, O and H atoms, with cyclic siloxanes beingespecially preferred. Examples of some highly preferred first precursorsinclude siloxanes selected from molecules with ring structures such as1,3,5,7-tetramethylcyclotetrasiloxane (TMCTS or C₄H₁₆O₄Si₄),octamethylcyclotetrasiloxane (OMCTS, C₈H₂₄O₄Si₄),tetraethylcyclotetrasiloxane (C₈H₂₄O₄Si₄), decamethylcyclopentasiloxane(C₁₀H₃₀O₅Si₅), trimethylcyclotrisiloxane, hexamethylcyclotrisiloxane,molecules of methylsilanes mixed with an oxidizing agent such as O₂ orN₂O or precursor mixtures including Si, O and C.

The second precursor is selected from the group comprising moleculeswith ring structures containing C and H atoms such as cyclichydrocarbons, cyclic alcohols, cyclic ethers, cyclic aldehydes, cyclicketones, cyclic esters, phenols, cyclic amines, or other O, N or Fcontaining cyclic hydrocarbons. More preferably, the second precursormolecule is a multicyclic (or polycyclic) hydrocarbon containing about 6to 12 carbon atoms, with preferably rings of 3 or more atoms. Preferredexamples include 2,5-norbornadiene (also known asbicyclo[2.2.1]hepta-2,5-diene), norbornylene 2,5-norbornadiene (alsoknown as bicyclo [2.2.1]hepta-2,5-diene), norbornane (also known asbicyclo[2.2.1]heptane). Other examples are tricyclo[3.2.1.0]octane,tricyclo[3.2.2.0]nonane, connected ring hydrocarbons such asspiro[3.4]octane, spirol[4.5]nonane, spiro[5.6]decane, and the like.Alternatively, cyclic hydrocarbons containing from 5 to 12 carbon atoms(cyclopentane, cyclohexane, and the like) and also cyclic aromatichydrocarbons containing 6 to 12 C atoms (benzene, toluene, xylenes, andthe like) may be used. Optionally, O or F atoms may be contained in themolecules, or molecules containing such atoms added to the precursormixture.

Especially useful, are species containing fused rings, at least one ofwhich contains a heteroatom, preferentially oxygen. Of these species,the most suitable are those that include a ring of a size that impartssignificant ring strain, namely rings of 3 or 4 atoms and/or 7 or moreatoms. Particularly attractive, are members of a class of compoundsknown as oxabicyclics. Among the readily available examples of these,are 6-oxabicyclo[3.1.0]hexane or cyclopentene oxide (bp=102° C. at 760mm Hg);

-   7-oxabicyclo[4.1.0]heptane or cyclohexene oxide (bp=129° C. at 760    mm Hg);-   9-oxabicyclo[6.1.0]nonane or cyclooctene oxide (bp=55° C. at 5 mm    Hg); and-   7-oxabicyclo[2.2.1]heptane or 1,4-epoxycyclohexane (bp=119° C. at    713 mm Hg). One highly preferred fused ring species that is employed    in the first embodiment of the present invention is cyclopentene    oxide (CPO).

The second precursor can also include a siloxane selected fromtetramethylorthosilicate (TMOS), tetraethylorthosilicate (TEOS),vinyltriethoxysilane, allyltrimethoxysilane, vinyltrimethoxysilane,allyltriethoxysilane, phenyltriethoxysilane, and phenyltrimethoxysilane.

The porous OSG material is formed by providing a pore forming materialsuch as a porogen during deposition. Although any deposition techniquecan be used in forming the OSG materials, the techniques disclosed inco-assigned U.S. Pat. Nos. 6,147,009, 6,497,963, 6,312,793, 6,441,491and 6,479,110, the entirety of each reference is incorporated herein byreference, are particularly preferred herein.

The various OSG dielectrics may be deposited within the same reactorchamber without the need of breaking vacuum, or the various OSGdielectrics may be deposited in separate reactor chambers.

The thickness of the non-porous OSG interlevel dielectrics 18 and 22 isgreater than that of the porous OSG etch stop layer 20. Typically, thenon-porous OSG dielectrics 18, 22 have a thickness from about 100 toabout 500 nm, while the porous OSG etch stop layer 20 has a thicknessfrom about 30 to about 150 nm.

After forming the various OSG dielectrics, at least one opening 24 isformed through layers 22, 20, 18 and 16 stopping on the conductiveregion 14. The at least one opening 24 formed in the second non-porousOSG dielectric 22 is typically wider than the opening formed in thefirst porous OSG dielectric 18. The wider opening formed in the secondnon-porous OSG ILD 22 is referred to herein as a line opening 26, whilethe narrower opening in the first non-porous OSG ILD 18 is referred toherein as a via opening 28.

The at least one opening 24 is formed by lithography and an etchingprocess in which a fluorocarbon-based plasma having a fluorine to carbonratio and at an ion current that selectively etches the non-porousorganosilicate glass interlevel dielectrics relative to the porousorganosilicate glass is employed. The term “fluorocarbon-based plasma”comprises any plasma that includes fluorine and carbon. One example of afluorocarbon-based plasma employed in the present invention is a plasmathat comprises CF₄ and C₄F₈. Other types of fluorocarbon-based plasmas,as discussed hereinbelow, are also contemplated herein.

The plasma which is generated using a plasma source from anyconventional plasma etching platform can be admixed with an inert gassuch, for example, He, N₂, Ar, Xe, Ne and mixtures thereof. Reducinggaseous radicals and/or oxidizing gaseous radicals may be present in thefluorocarbon-based plasma as well. A gas-phase fluorine to carbon, F:C,ratio from about 1.5:1 to about 4:1 (assuming quasi-complete gasdissociation) is typically employed in the present invention, and theion current of the etch tool is typically from about 1 to about 20(relative units); where 1 denotes the threshold ion energy for ionenhanced (assisted) desorption (etching) of adsorbates from thedielectric surface to occur.

Specifically, in this embodiment of the present invention, the use of aporous OSG material having a carbon content that exceeds that of anon-porous OSG ILD facilitates the possibility of utilizing the porousOSG material as an etch stop layer by operating in a plasma processingregime that enables etching of the non-porous low-k film selective tothe porous film. Such a unique and seemingly counterintuitive feature ismade feasible in the present invention by preselecting (1) the gas-phasefluorine to carbon (F:C) ratio (degree of gas dissociation) and (2) theion current incident on the wafer surface such that the non-porous OSGfilms is selectively etched as compared to the porous OSG film.

The proposed generic etch mechanism for OSG films, i.e., SiCOH, in afluorocarbon-based plasma can be summarized by the following unbalancedequations:SiCOH_((s))+CF_(x(g)), F_((g))

SiF_((g)), CO_((g)), COF_((g)), HF_((g))(x=1-3)+N_((g)), O_((g))

CN_((g)), CO_((g)), OH_((g))

The role of gas phase carbon, as illustrated above, is to “scavenge”oxygen within the SiCOH film as various gaseous products; while carbonin the film is scavenged by some reducing (N₂ or H₂) or oxidizing (O₂)gaseous radicals. However, by tuning the gas-phase F:C ratio (degree ofgas dissociation), one can essentially overwhelm the SiCOH film withvarious gaseous molecular carbon (CF, CF₂ etc) radicals such that alloxygen within the film is completely removed with the excess gaseousmolecular carbon species remaining forming a SiC-like layer at thesurface impeding further etching, i.e., inducing the so-called “etchstop” phenomenon. It is thus feasible, if the carbon content of theporous OSG material is greater than the carbon content in the non-porousOSG film to tune the gas-phase F:C ratio such that the non-porous filmetches by the generic mechanism outlined in the above equations whereasthe porous film undergoes so-called etch stop.

To enable this phenomenon, it is not sufficient to only have areasonably low gas-phase F:C ratio (minimal gas dissociation), butadditionally requires a minimal ion current (on the order ofapproximately the ion density x ion energy) incident on the wafersurface. Since conventionally employed porous OSG film's (k ofapproximately 2.2) are typically at least 30% fractionally porous; evenif the gaseous F:C ratio is such that the film should undergo etch stopin theory; if the ion current to the wafer is such that sputtering ofthe SiC-type monolayer thick film at the surface of the porous low-kfilm exposes underlying pores, etching of the film will proceed at somefinite rate. It is, thus, also necessary to tune the ion current to thewafer below a critical threshold such that etching of the non-porousfilm is still enabled whereas that of the porous film “ceases”.

Typical plasma processing conditions on a commercial dual frequencycapacitively-coupled BEOL etch platform that will achieve the aboveselective etching of a non-porous OSG film with respect to a porous OSGfilm are: 40 to 200 mTorr pressure; 150W₂₇ to 450W₂₇; (where W₂₇ and W₂refer to the deposited power for 27 MHz and 2 MHz frequencies,respectively) 0 to 100W₂; 50 to 200 sccm Ar; 50 to 200 sccm N₂; 3 to 8sccm C₄F₈; 5 to 20 sccm CF₄. More typical ranges for these parametersare: 50 to 90 mTorr pressure; 250W₂₇ to 350W₂₇; 0 to 50W₂; 75 to 125sccm Ar; 50 to 150 sccm N₂; 4 to 6 sccm C₄F₈; and 5 to 15 sccm CF₄. Etchselectivities on the order of 4.4 to 3.0:1 are achieved within theseprocessing conditions. The tolerance in each of these parameters forachieving such selectivity values are given in Table I below coupledwith the potential function of each of these parameters.

TABLE I Plasma Parameter Tolerance Range Function 27 MHz Power (W) 200to 400  Gas-Phase FC Ratio/Ion Current  2 MHz Power (W) <100 Ion CurrentPressure (mT) 70 to 140 Gas-Phase FC Ratio/Ion Current C₄F₈ Flow (sccm)4 to 10 Gas-Phase FC Ratio CF₄ Flow (sccm) 7 to 20 Gas-Phase FC Ratio Ar50 to 200 Ion Current

It is significant to note, though not demonstrated here, that othermono- and poly-carbon-type fluorocarbon molecules can potentiallyachieve similar selectivities of etching a non-porous SiCOH film (k˜2.8to 3.1) selective to a porous SiCOH film (k≦2.2); namely the replacementof CF₄ with CHF₃, CH₂F₂, CH₃F, or combinations of these and thereplacement of C₄F₈ with C₄F₆, or C₅F₈, or C₂F₆, C₃F₆, or combinationsof these.

After etching, a conductive metal, which can be the same or differentmaterial as conductive region 14 is formed in the at least one opening24. A preferred metal for filling the opening 24 is Cu. The conductivemetal is formed within the at least one opening 24 utilizing aconventional trench fill process such as chemical vapor deposition(CVD), plasma-assisted CVD, plating, sputtering, chemical solutiondeposition and other like deposition processes. A planarization processsuch as chemical-mechanical polishing (CMP) or grinding typicallyfollows the trench fill process.

An optional liner material, not shown, can be formed within the etchedtrench prior to trench fill. The optional liner material preventsdiffusion of the conductive metal into the dielectric layers. Someexamples of such liners include, but are not limited to, TiN, TaN, Ti,Ta, W, WN, Cr, Nb and other like metal diffusion barrier liners andcombinations thereof. The optional liner can be formed in the trenchusing well known deposition processes including, for example, CVD,plasma-assisted CVD, sputtering, plating and chemical solutiondeposition.

The corollary of the first embodiment mentioned above is the use of adense low-k OSG dielectric as a hardmask layer for dual damascene builtin a porous low-k OSG material. In this embodiment of the presentinvention, the porous OSG has a C content that also exceeds that of thenon-porous OSG. The potential use of porous low-k OSG materials for 65nm and subsequent BEOL technologies also introduces the concept of lineheight control and consequent line resistance variance. Since typicalprocessing conditions would etch the dense low-k OSG dielectric hardmaskfaster than the underlying porous low-k OSG material; this issue isperhaps made even more severe for these technologies. However, utilizingthe conditions described herein, one can selectively etch the dense,i.e., non-porous, low-k OSG hardmask selective to the underlying porouslow-k OSG material effectively stopping on the latter. Thus, thesubsequent application of the specifically tailored porous ILD etchchemistry to create the desire line structure will potentially result ina reduction in line height variations and line resistance variance,perhaps without the use of an ESL for the porous low-k material. Thisonce more seemingly counterintuitive design will improve deviceperformance (reduced k_(eff)) and functionality (uniform line heights).

FIGS. 3A-3B illustrate the second embodiment in which a non-porous OSGhardmask is used as an etch stop for a porous OSG dielectric. In FIG.3A, reference numeral 12 denotes a substrate and reference numeral 14denotes a conductive region. The reference numerals are the same asdescribed above in the first embodiment; therefore the materials andmethods described above are applicable here as well. A dielectric cap 16(see above definition and description) is then formed atop the exposedsurfaces of substrate 12 and conductive region 14.

In the second embodiment, a porous OSG ILD 50 and a non-porous OSGhardmask 52 are then formed using the technique and materials describedabove in connection with OSG layers 18, 20 and 22. In the secondembodiment, the porous OSG ILD 50 also has a carbon content that exceedsthe non-porous OSG hardmask 52. In this embodiment, porous OSG ILD 50 isthicker than non-porous OSG hardmask 52. The thickness of the porous OSGILD 50 is typically from about 60 to about 280 nm, while the thicknessof the non-porous OSG hardmask 52 is from about 30 to about 50 nm.

Next, oxide hard mask 54 is formed atop the non-porous hardmask 52 andan opening that is filled with a planarizing dielectric 56 is thenformed by lithography, etching and deposition. The etching step includesany conventional etching process. Note that the etching processmentioned above which includes the fluorocarbon-based plasma etch canalso be employed at this point of the second embodiment of the presentinvention. The planarizing dielectric includes any material that canserve as a planarizing layer including for example, a non-photosensitiveorganic cross-linked polymer.

After forming the planarizing dielectric 56, an oxide cap 58 such as alow temperature oxide and an optional antireflective coating 60 areformed by known deposition methods. A patterned photoresist 62containing a line pattern is formed by deposition and lithography.Several prior art etch processes are then used to etch layers 60, 58,and 56 which is subsequently followed by the inventive etch to processlayers 54 and 52 selectively to layer 50. This latter etching process ina fluorocarbon-based plasma having a fluorine to carbon ratio and at anion current that selectively etches the non-porous organosilicate glasshardmask relative to the porous organosilicate glass ILD (combined withthe prior art processes aforementioned) are used to form the structureshown in FIG. 3B.

FIGS. 4A-4B actual cross sectional scanning electron micrographs (SEMs)of various dual damascene interconnect structures built in a porous OSGdielectric with TEOS and SiCOH hardmask showing a 28 nm line heightsubsequent to 45 seconds of the inventive trench etch and a 41 nm lineheight subsequent to 60 seconds of the inventive trench etch,respectively. These structures were formed utilizing the proceduredescribed above in regard to the second embodiment of the presentinvention. The non-porous OSG ILD in this specific trench etch chemistryused to create these SEMs etched at a rate of ˜4 nm/s. The two SEMsclearly illustrate that the porous OSG ILD etch rate in this specificetch chemistry is ˜1 nm/s illustrating a selectivity of this chemistryof ˜4:1 for the non-porous OSG ILD relative to its porous counterpart.

While the present invention has been particularly shown and describedwith respect to preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formsand details may be made without departing from the spirit and scope ofthe present invention. It is therefore intended that the presentinvention not be limited to the exact forms and details described andillustrated, but fall within the spirit and scope of the appendedclaims.

1. A method of forming a pre-metallized interconnect structurecomprising: providing a structure comprising an etch stop layercomprising a porous organosilicated glass located between a firstnon-porous organosilicate glass interlevel dielectric and a secondnon-porous organosilicate glass interlevel dielectric, said porousorganosilicate glass having a carbon content that is greater than thecarbon content in the first and second non-porous organosilicate glassinterlevel dielectrics; and patterning said structure to provide anopening that extends through the structure, said patterning comprisinglithography and etching, wherein said etching is performed in afluorocarbon-based plasma having a fluorine to carbon ratio and at anion current that selectively etches the non-porous organosilicate glassinterlevel dielectrics relative to the porous organosilicate glass,whereby a material of said second non-porous organosilicate glassinterlevel dielectric is removed selective to said porous organosilicateglass during said etching through formation by said fluorine-basedplasma of a SiC-like film that impedes further etching at a surface ofsaid etch stop layer.
 2. The method of claim 1 wherein said providingstep comprising at least a deposition process in which a first precursorcomprising atoms of Si, C, O and H is employed.
 3. The method of claim 1wherein said providing step further comprises a second precursorcomprises C and H atoms, and optionally N, O and F.
 4. The method ofclaim 1 wherein said fluorocarbon-based plasma comprises a mixture ofCF₄ and C₄F₈, or other gases that contain fluorine and carbon.
 5. Themethod of claim 1 wherein said fluorine:carbon ratio is from about 1.5:1to about 4:1 and said ion current is from about 1 to about 20 (relativeunits); where 1 is defined as the threshold ion energy for ion enhanced(assisted) desorption (etching) of adsorbates from a dielectric surfaceto occur.
 6. The method of claim 1 wherein said fluorocarbon-basedplasma etch is performed at a pressure from about 40 mTorr to about 200mTorr.
 7. The method of claim 1, wherein said SiC-like film is derivedfrom a portion of said etch stop layer by removal of all oxygen fromsaid portion by said fluorocarbon-based plasma.
 8. The method of claim7, wherein said second non-porous organosilicate glass interleveldielectric does not go through an etch-stop while said portion of saidetch stop layer goes through an etch stop.